We are a group of scientists based at the University of Reading’s School of Biological Sciences working on the impact of pollutants on freshwater invertebrates. Our work has included looking at the effect of pesticides, herbicides, drugs, pond dyes and now microplastics on non-target freshwater organisms, i.e. the chemicals they are exposed to are not purposely applied to control them. I have also had a long career working on mosquitoes, particularly looking at their ecology and resistance to insecticides. This paper is therefore one of a series which has pulled together my ecotoxicology research and my research on mosquitoes. Over the past three years I have been working with PhD candidate Rana Al-Jaibachi, studying the impact of microplastic beads on water fleas, mosquitoes and general pond life.
The article is a proof-of-concept piece which was undertaken to see whether there was any evidence that microplastics could be transferred between life stages once ingested. We already knew that mosquito larvae would eat the microplastic beads and that they would most likely excrete them from their guts. Mosquitoes have four feeding larval stages, a non-feeding pupal stage and finally the flying adult. We thought it likely that the final fourth instar larva might retain microplastics in its guts and transfer them to the pupae, but were surprised at the high proportion that were retained, especially since part of the larval gut is dissolved in the pupa. Even more surprising was the retention of the plastics in the adult gut and their location in the mosquito version of a kidney.
These results have some worrying implications and this paper is intended to highlight the issue. We know that there are areas of high microplastic pollution in parts of the world where mosquitoes or other insects with similar life cycles are found. It is highly likely that flying insects emerging from these lakes or ponds contain microplastics.
So why does this matter? The first reason is that it represents a new pathway of plastic pollution into the environment. Whilst small numbers of beads are unlikely to impact either the mosquito life cycle or any animals that eat them, we should be concerned that they could be bioaccumulated in the food chain. The second is that microplastics can act as carriers for the transfer of harmful synthetic organic compounds from the environment to the animal that ingests them. Whilst the plastic itself might have little toxicity, a period in a polluted environment could mean that it has picked up toxic chemicals and effectively concentrated them on its surface.
We chose Biology Letters because it publishes high impact short publications. We were very happy with the publishing experience which was rapid and efficient. We were also impressed with the promotion of the paper and particularly with the communication between the journal and our press office. We have published a piece of follow-up work in Science of the Total Environment which shows that microplastics don’t impact on mosquito mortality. We have also shown that microplastics in mosquito larvae can be transferred to an insect predator, and that microplastics are eaten by mosquito larvae in ponds contaminated with microplastic beads (currently unpublished).
Clearly the next step would be to undertake some field work to try and capture flying insects as they emerge from a heavily polluted lake. We hope that other research groups take on the challenge of detecting microplastics in the food chain.